The present invention relates to a method for informing a mobile terminal about the properties of a communication network, which communication network comprises at least two base transceiver stations which form at least two cells whose properties affect the functions available in the mobile terminal within the cell, and in which the current serving base station is at least one base station of the cell, through which the connection between the mobile terminal and the communication network is maintained. The invention also relates to a system comprising a mobile terminal, means for informing the mobile terminal about the properties of a communication network, which communication network comprises at least two base transceiver stations which form at least two cells whose properties affect the functions available in the mobile terminal within the cell, and in which the current serving base station is arranged to be at least one base station of the cell, through which the connection between the mobile terminal and the communication network is arranged to be maintained. The invention further relates to a mobile terminal comprising means for receiving information about at least one property of a communication network in the mobile terminal, which communication network comprises at least two base transceiver stations which form at least two cells whose properties affect the functions available in the mobile terminal within the cell, and in which the current serving base station is arranged to be at least one base station of the cell, through which the connection between the mobile terminal and the communication network is arranged to be maintained.
In addition to a conventional circuit switched connection, the option of a packet switched connection has been developed for mobile communication systems, such as the GSM mobile communication system. In the GSM mobile communication system, such a service is the so-called general packet radio service (GPRS). The GPRS makes it possible to use e.g. the Internet Protocol (IP) as well as the X.25 communication protocol, to transmit short messages (SMS, Short Message Service), to transmit e-mail, as well as to use WAP applications (Wireless Application Protocol). Such a packet data transmission connection provides a communication method which is more efficient than the circuit switched connection, particularly for asynchronic data transmission, because to use the packet switched connection, the resources of the mobile communication system are not allocated for the whole time of the connection but only for the time needed for the transmission of the packets. In the circuit switched connection, however, the connection is allocated for the whole time when it is on. By means of the packet switched connection, the user of a mobile terminal can, for example, keep an e-mail application activated all the time, wherein the user will notice an incoming e-mail message at once. Because the packet switched connection only allocates resources according to the need, it may also be less expensive as to the call costs when compared with a situation of using a circuit switched connection.
In the GPRS system, three operating modes are defined for the mobile terminal: class A, class B, and class C. The mobile terminals can be classified into these categories according to the type of packet network properties implemented in them. Mobile terminals of class A can employ GPRS services and other GSM services simultaneously. Mobile terminals of class B can simultaneously monitor signals on the control channels of the GPRS network and the GSM network, but they can only use either GPRS services or GSM services at a time. Mobile terminals of class C can use a circuit switched connection and a packet switched GPRS connection, but not simultaneously.
In practice, a mobile terminal of class B can receive messages related to the setting up of a circuit switched connection also when the mobile terminal is using GPRS services, for example when a packet connection is active for using a WAP browser. The mobile terminal can then e.g. receive a message informing about an incoming call (CS paging), but it cannot operate in a circuit switched connection and in a packet switched connection at the same time. Thus, in a situation of an incoming message for the mobile terminal, related to a circuit switched connection, the packet connection is set pending for the time of receiving the message and for the time of a circuit switched connection which is possibly formed, until the circuit switched connection is terminated. In an ideal situation, this means that the mobile terminal can change its mode between the packet switched connection and the circuit switched connection and, after the change, continue from the mode in which the mobile terminal was at the time of the interruption. However, it has been found in practice that applications using a packet switched connection, such as e-mail or e.g. the FTP application used for the transmission of data files, are disconnected even after a relatively short interruption of the connection. For example, in some known e-mail protocols, such as POP3 (Post Office Protocol) and IMAP4 (Internet Message Access Protocol), messages must be transmitted at intervals during the connection, to prevent disconnection. Such a property is used e.g. to prevent the connection from being left redundantly active. If the e-mail server does not receive such a message within a predetermined time, the server will determine that the communication has been cut off or the terminal is no longer in operation, wherein the server disconnects the connection. When using the POP3 protocol, the connection can be disconnected even after an interruption of about 10 minutes, and when using the IMAP4 protocol, an interruption of about 30 minutes may cause disconnection of the e-mail connection. After the disconnection, the user must re-establish the e-mail connection and give his/her user identification and password, which will retard the use of the e-mail application.
Thus, in a situation in which the packet switched connection is active in the mobile terminal and there is an incoming call for the mobile terminal, the packet connection is set pending. Thus, the above-mentioned messages for maintaining the packet connection cannot be transmitted from mobile terminals of prior art, wherein the packet connection may be disconnected. The packet connection may be disconnected even during a considerably shorter call than the above mentioned 10 or 30 minutes. This is possible e.g. when there is an incoming call just a moment before the message to maintain the connection is due for transmission. It is even possible that the connection is disconnected before the user has had time to answer the call.
The above-mentioned problem also occurs in a situation in which the user of the mobile terminal sets up a circuit switched connection, e.g. a voice call, in a situation in which the packet connection is active in the mobile terminal. Also in this case, the circuit switched connection prevents the transmission of messages to maintain the packet connection, which may result in the disconnection of the packet connection during even a short call. One possibility to prevent the disconnection of the packet connection is thus to start the call first after the message to maintain the packet connection has been transmitted. However, the user does not necessarily even know about such a property, and on the other hand, it is not appropriate to presuppose that the user always remembers, when making a call, to first transmit a message to maintain the packet connection.
In practice, different mobile communication networks may also have different properties. Thus, some mobile communication networks implement the properties of all the above-mentioned classes A, B and C, but some mobile communication networks implement the properties of only one such class, e.g. class C. Moreover, the properties of even the same mobile communication network may change when moving from the range of one cell to the range of another cell. For example, in third generation mobile communication networks under development, such as the UMTS (Universal Mobile Telecommunication System), quality of service levels are defined for various connections. However, all the defined quality of service levels are not necessarily implemented in all the cells of such a mobile communication network. Thus, situations may occur, in which all the services available for a mobile terminal cannot be guaranteed for it. As a result, an active connection may be disconnected when the mobile terminal moves from the range of one mobile communication network to the range of another mobile communication network, or even from the range of one cell to the range of another cell. For example, if the user has a video call active within the range of a cell, and if the mobile terminal moves to the range of such a cell which does not support the video call property, the video call will be disconnected. Such a disconnection may cause considerable harm for the user of the mobile terminal, because the disconnection cannot be anticipated in solutions of prior art.
In mobile communication networks, a cell refers to the geographical area in which the signal of the base station of the mobile communication network is sufficiently strong to maintain a connection between the mobile communication network and the mobile terminal. For example, in GSM mobile communication networks, the radius of such an area covered by the cell is typically in the order of 35 km around the base station. However, in practice, the size of the cell may be affected by topography and climatic conditions, wherein the cell may be locally smaller or larger than the average cell size. Furthermore, particularly in urban areas, the cell size can be reduced and several cells can be provided in urban areas, wherein the capacity of the mobile communication network can be increased in such areas to some extent.
In this description, a base station via which the mobile terminal communicates with the mobile communication network is referred to as a serving base station. Such a serving base station is not necessarily always the base station closest to the mobile terminal. The serving base station may also be changed, for example, in a situation in which the mobile terminal moves from the range of one cell to the range of another cell. If the serving base station is not the base station closest to the location of the mobile terminal, the mobile communication network can, for example, reduce the transmission power of the closer base stations and/or increase the transmission power of the serving base station, so that the signals of the closer base stations would not disturb the connection between the serving base station and the mobile terminal. In some cases, the connection between a more distant serving base station and the mobile terminal can also be arranged in such a way that the signals to be transmitted in the connection between the serving base station and the mobile terminal are linked via one or more base stations. In some mobile communication networks, such as the UMTS (Universal Mobile Telecommunication System), there can be several serving base stations simultaneously, wherein substantially the same information is transmitted from several base stations to the mobile terminal. Such a group of serving base stations is also called an active set.
The communication network can also be another communication network, such as a wireless local area network WLAN. Thus, also the base station can be other than a base station in a mobile communication network, such as an access point in a wireless local area network, or the like. Furthermore, the communication network may comprise several communication networks which may also be different from each other.